In recent years, there can be seen advancement in the density increase of an electronic circuit device, and an attention is paid onto an electronic circuit device, in which a plurality of ball electrodes are arranged in a peripheral configuration or an array configuration to connect a semiconductor package and a printed wiring board.
However, it is difficult to visually confirm the connection state of ball electrodes that are disposed between the semiconductor package and the printed wiring board from outside.
For that reason, as a method of confirming the connection state of ball electrodes, there is known a method of applying a feature including a recess or intrusion to the shape of a pad to which a ball electrode is to be connected and determining the connection state based on the shape of a shaded image (transmission shaded image) of the ball electrode obtained by x-ray transmission (or x-ray fluoroscopy) (see Japanese Patent Application Laid-Open No. H09-219583 and Japanese Patent No. 3601714).
Further, there is also known a technology of making different from each other the shapes in which an electrode pad provided on a lower surface of an electronic circuit board and a foot pattern provided on an upper surface of a board are connected through intermediation of a ball electrode to easily confirm the connection state between the upper and lower members by one-time x-ray inspection (Japanese Patent Application Laid-Open No. H09-051017).
However, in recent years, in order to further advance density increase, attention is paid to an electronic circuit device in which a semiconductor package and a printed wiring board which are connected by ball electrodes are not disposed in a planar configuration as in the conventional art, but are stacked in three or more layers.
In such an electronic circuit board, because the shaded images obtained by transmission of ball electrodes that are disposed in a stacked fashion are displayed in a superimposed manner, there is still an unsolved problem that the connection state of the ball electrodes cannot easily be confirmed by the above-mentioned procedure.
Also, in the electronic circuit device having the stack structure, it is difficult to radiate a heat generated in the electronic circuit device to outside as compared to the conventional electronic circuit device having the planar arrangement. Therefore, the electronic circuit device needs to have such a stack structure as to efficiently radiate heat to outside. In general, the ball electrode is smaller in thermal conductivity than other members and therefore serves as a good radiation path.
However, in order to image the connection state of the ball electrodes by x-ray inspection, when the electrode pads and the ball electrodes which are provided in different layers are disposed in a nested manner, a heat generated in the semiconductor package or the printed wiring board needs to excessively pass through the board, with the result that the heat generated in the interior of the stack structure is difficult to be radiated to outside.